Method of converting metal powder into flake



y 0, 1963 D. K. WORN 3,099,080

' METHOD OF CONVERTING METAL PQWDER INTO FLAKE Filed June 18, 1958 2 Sheets-Sheet 1 DAVID KENNETH WORN INVENTOR.

BY Gig M ATTORNEY July 30, 1963 D. K. WORN 3,099,080

METHOD OF CONVERTING METAL POWDER INTO FLAKE Filed June 18, 1958 2 Sheets-Sheet 2 FIG. 2

DAVID KENNETH WORN INVENTOR.

ATTORNEY United States Patent 3,099,080 METHOD OF CONVERTING METAL PGWDER INTO FLAKE David Kenneth Worn, Soiihull, England, assignor to The International Nickel Company, Inc, New York, N.Y., a corporation of Deiaware Filed June 18, 1958, Ser. No. 742,846 Claims priority, application Great Britain July 1, 1957 1 Claim. (Cl. 29-420) The present invention relates to powder metallurgy and, more particularly, to an apparatus and method for producing special metal powders having improved properties.

Heretofore, metal powders having a flaky shape have usually been produced from certain very malleable metals the powder particles being of considerable size. In the art of powder metallurgy, fine metal powders are commonly used and there is sometimes an advantage in converting these powders into flakes. We have found that for certain metallurgical purposes, metal powders made from relatively hard and relatively high melting point but malleable metals and alloys, having a flaky shape, will impart superior properties to certain finished materials produced by powder metallurgical methods from such powders. However, suitable methods and/ or apparatus designed to economically produce powder having a flaky shape from fine powder and especially from refractory metals and alloys do not now exist. Although attempts were made to overcome the foregoing difliculties and other difficulties, none, as far as I am aware, was entirely successful when carried into practice on an industrial scale.

It has now been discovered that certain refractory metal powders that is to say powders made from relatively hard metals and alloys; powders such as iron powder made by the carbonyl process and alloy powders such as nickelchromium and iron-chromium made by atomisation (these powders are indeed hard when compared with inter alia the powders of copper, aluminum, silver and gold), can be provided having improved properties and shape which are then useful for the production of new materials.

It is an object of the present invention to provide an apparatus for producing the said refractory metal powders having a particular shape.

The invention also contemplates providing a novel apparatus for flattening the said refractory metal powders.

Still another object of the invention is to provide a method of making the said refractory metal powders having a special flakelike shape.

Other objects and advantages will become apparent from the following description taken in conjunction with the accompanying drawing in which:

FIGURE 1 is a drawing of one embodiment of an apparatus designed to produce the special powder in ac cordance with the invention, and

FIGURE 2 depicts an arrangement of a spring system for regulating the applied load or force on the powder while it is being flattened in the apparatus illustrated in FIGURE 1.

Generally speaking, the apparatus for treating refractory metal powder consists essentially of one or more sets of rolling or flattening units consisting of a plurality of rollers lying between and bearing upon inner and outer races, and means for causing the powder particles to pass between the races and to be rolled between the rollers and the races in so doing. One of the races ro tates during operation and the powder is caused to pass between the rollers and the races enough times to ensure that all the particles are transformed from the rougly equiaxed form in which metal powders are frequently produced to the desired flake form. The process may be carried on continuously, e.g. by the provision of an 3,fl99,080 Patented July 30, 1963 ice adequate number of rolling units, i.e. sets of rollers running between inner and outer races, in series through which the powder is passed in succession, or by repeatedly circulating the powder through one rolling unit.

Thus, the novel apparatus contemplated herein for converting substantially equiaxed metal powder to the form of flakes comprises a plurality of rollers, inner and outer concentric races bearing upon said rollers, means for driving at least one of said races, means for feeding powder between said rollers and said races and means for removing powder. The rollers are advantageously tapered, and means are provided for regulating and/ or adjusting radial pressure applied between the races and rollers. The rollers are rotatable about their own axes and about a central axis such that said axes of the rollers follow a circular path intermediate the inner and outer races which are concentric to said axis and which have faces bearing on said rollers.

In carrying the invention into practice, it is preferred to use an apparatus such as that shown in FIGURE 1 of the accompanying drawing. This apparatus comprises a cylindrical casing 1 with a hopper-shaped bottom 2. A central vertical shaft 3 driven by driving means (not shown in the drawing) through a gearwheel 4 which drives the shaft, said shaft then passes through a spider 5 in the top of the casing 1 and is keyed to the inner races 6 and 7 having outer races 8 and 9 held by a ring 10 fixed in the casing 1. Tapered rollers 11 are arranged between the inner and outer races, all the center lines of each set of rollers meeting on the axis of the shaft 3. In order to cause a heavy radial load to be applied to the powder being passed between the rollers and races of the apparatus, an axial force is applied to races 8i and 9 and this is imparted to the powder passing between the rollers and the races, as illustrated in FIGURE 2, by a spring system comprising spring 17 and castellated ring nut 18 designed to cause a heavy radial load, i.e. force, to be applied to the powder. As can be seen in FIGURE 2, the action of screwing down the nut 18 forces down spring 17 and pushes races 8 and 9 towards each other thus causing a powerful force to act on the races and to be exerted against the powder particles being rolled.

Advantageously, the powder to be rolled is first sieved to give particles of less than about 50 microns in diameter. The graded powder is fed as a slurry with oil or other liquid through an inlet 12 and in passing between both the races 6 and 8 and the races 7 and 9 is rolled by the rollers 11. Since some of the powder particles fall be tween two adjacent rollers and are not therefore transformed to flake immediately, means are provided to draw the slurry through the bottom 2, e.g., by a pump 13. The slurry or powder is then delivered to a second inlet "14 to pass, recycle or recirculate as many times as necessary through the apparatus. When substantially all the powder particles are rolled to flake form, the slurry is removed through a pipe 15.

An agitator 16 is carried on the bottom of the shaft 3 to mix the particles before they are recirculated. A1- ternatively, a classifier may be incorporated in the circuit to continuously remove the particles reduced to flake form.

The rollers 11 may be very small, say between about 3 mm. and about 10 mm. in diameter, advantageously about 5 mm. in diameter or less, and when subjected to high radial loading, e.g., by the application of an axial force to the races, are found to reduce particles of, for example, nickel-chromium alloy powder averaging 50 microns in diameter to flakes about 1 micron thick without difiiculty. The rollers are preferably about 10 mm.

to about 30 mm. long, e.g., about 17 mm. The outer races preferably are at least about mm. up to about 200 mm. in diameter, i.e., have a minimum diameter at least about 8 times greater than the maximum diameter of the rollers used therewith. The rolling faces provided on each race will have a shape to match the shape of the roller used therewith. The rollers are advantageously tapered and, in that case, the bearing faces of each race are also tapered in the same manner to provide a bearing between the rollers and the races. A complete mill may comprise several units such as that shown in FIG. 1 linked together on one axis. In this case it is sometimes desirable that each single outer race of the tapered roller bearing be adjustable individually so that the pressure can be increased against the powder particles as they become progressively flattened. Other forms of rollers may be used, i.e., the rollers may also be barrel shaped with one end smaller than the other. Again, the rollers may be similar to the rollers used in thrust bearings in which the rollers have a curved generatrix and are basically of a tapered shape. Each set of rollers shown in the drawing as equally disposed in a radial direction about the central vertical driving shaft in the same horizontal plane and at a substantially equal angular spacing together with the cooperating races having a frusto-conical bearing surface form a rolling unit and the mill advantageously consists of a number of rolling units in series so as to ensure that the powder particles which issue at the lower end have been changed from the spherical into the flake form. It is likewise possible to have a completely enclosed apparatus and to circulate the powder through the apparatus using a carrier gas.

The invention herein described contemplates an improved apparatus for treating metal powders, particularly refractory metal powders in a particular manner thereby imparting to the powder a thin flaky shape. Although by using the apparatus described herein a flake powder having a thinness of about 0.5 micron or even less can be produced, for many purposes powder having an average thinness of between about 1 and 2 microns is satisfactory. In general, the flake powder will have an average thinness less than about 2 microns. The treatment herein described has proved particularly useful in connection with powder made from certain refractory metals such as iron and nickel and alloys of cobalt, nickel, and iron with each other and with carbon, chromium, aluminium, beryllium, manganese, molybdenum, silicon, tungsten, vanadium, etc.,. and including stainless steels, nickel-chromium alloys, such as nickel-chromium-iron alloys. If the powder to be rolled is a very hard and abrasive powder, the rollers and races can advantageously be made of sintered hard metals, e.g., tungsten carbide with cobalt.

In some cases, e.g., if the powder must be coated by chemical reaction as in the case of certain iron and iron alloy powders on which an electrical insulating coating of'sulfide is to be formed, it may be advantageous to use a stream of carrier gas containing a reagent, e.'g. hydrogen sulfide, to circulate the powder through the apparatus.

For the purpose of giving those skilled in the art a better understanding of the invention, the following illustrative example is given:

Example An atomised powder made from a nickel-chromium alloy containing about 20% of chromium, about 60% of nickel, about 20% cobalt was used as the starting powder. The powder was sieved to give basically spherical particles of less than 50 microns in diameter and then mixed with a thin oil to form a slurry. The central shaft was turned at a speed of about 500 r.p.m. for about 10 hours. During this time, the slurry was given a multiplicity of passes through the mill shown in the accompanying drawing until the powder was in a ilake form with an average flake particle thickness of approximately 2 microns. It will be appreciated that the time of treatment required to produce this particular flake could be reduced considerably by operating several rolling units in tandem on one axis.

The present invention is particularly useful in treating refractory metal (alloy) powders used in the production of new materials which require the inter-leaving of flakelike powder particles.

It is to be observed that the present invention provides for an improved apparatus for treating refractory metal powders so as to produce powder particles having a thin flaky shape and an average thickness not greater than about 5 microns, e.g., about 0.5 to about 2 microns, and one specific embodiment of said apparatus comprises a cylindrical casing having a central shaft passing through said casing and being connected to a plurality of inner races adapted and designed to cooperate with corresponding outer races, rollers between the races, means for driving at least one of said races, an inlet adapted to feed powder between the races and the rollers, means to draw the powder through the apparatus, means to recirculate the powder through the apparatus, an outlet to remove the treated powder, and means to cause a heavy radial load or force to be applied to powder passing between the rollers and races. Likewise, at least one of the races is adjustable to provide the required radial force or load to flatten powder passing between the races and rollers.

Furthermore, the invention provides for a method for producing flake shaped refractory metal powder having a thickness up to about 5 microns, e.g., between about 0.5 micron and about 2 microns, comprising the steps of sieving a refractory metal powder to obtain a fraction thereof comprising substantially spherical particles having an average particle size less than 50 microns, subjecting said powder to a plurality of flattening operations by introducing said powder into a rolling zone, said rolling zone being bounded by a pair of spaced races bearing upon a plurality of rollers having a substantially smaller diameter than said races, and circulating said powder through said rolling zone to roll said powder into a flakelike form having a thickness not exceeding 5 microns. The powder may be fed as a slurry with oil or other liquid or may be carried through the apparatus in a stream of gas. If the powder is to be coated, the carrier gas may contain a reagent,'e.g., hydrogen sulfide.

It is to be noted that the method and apparatus contemplated in accordance with the present invention is not to be confused with the method and apparatus'used to produce certain highly malleable metal powders used for paints or pigmentation, formerly called bronze powders, which are presently produced in ball mills, eddy mills, stamp mills, attrition mills or by the so-called Hametag process. The methods and apparatus used to produce such powders are not satisfactory for the production of the refractory metal powders such as those treated in accordance with the present invention.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to Without departing from the spirit and scope of the invention, as those skilled in the art will readily understand. Such modifications and variations are considered to be, within the purview and scope of the invention and appended claim.

I claim:

An improved process for producing discrete, fiat, flakelike particles having a maximum thickness of about 2 microns which comprises providing a slurry of metal powder in an oily liquid carrier, said powder being of metal selected from the group consisting of iron, nickel and alloys thereof including stainless steel, nickelchromium alloys and nickel-chromium-iron alloys and comprised of substantially spherical particles having a diameter less than about 50 microns, passing said slurry at least once through a rolling zone having a length of about 200 to about 600 times the maximum diameter of said powder particles and said slurry passing in a direction parallel to the length of said zone, said rolling zone being provided by a plurality of tapered rolls bearing against concentrically disposed races, subjecting said powder to a heavy radial load to accomplish a plurality of flattening operations thereon during a pass through said rolling zone, and thereafter separating metal from said slurry to recover a powder comprising discrete, flat, flake-like particles or said metal having a thickness of about 0.5 to about 2 microns.

964,024 Hotchkiss July 12, 1910 6 Kramer Nov. 24, 1931 Boothman Oct. 22, 1935 Boothman Oct. 22, 1935 Langbein- June 11, 1940 Ziehl Mar. 3, 1942 Klock Nov. 25, 1947 Traylar Mar. 15, 1949 Gaut et a1 Sept. 21, 1954 Golwynee Apr. 2, 1957 Hannon Nov. 25, 1958 Adams et a1 Dec. 16, 1958 

